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    SubjectRe: Fw: crash on x86_64 - mm related?
    Linus Torvalds <torvalds@osdl.org> wrote:
    >
    >
    >
    > On Sun, 8 Jan 2006, Ryan Richter wrote:
    > >
    > > Kernel BUG at mm/swap.c:49
    >
    > Well, it sure triggered.
    >
    > > Process taper (pid: 4501, threadinfo ffff8101453d8000, task ffff81017d0143c0)
    > > Call Trace:<ffffffff8028c614>{sgl_unmap_user_pages+124}
    > > <ffffffff8028834d>{release_buffering+27}
    >
    > and it's that same sgl_unmap_user_pages() that keeps on triggering it.
    >
    > Which was not what I was hoping for. I was hoping we'd see somebody _else_
    > decrementing the page count below the map count, and get a new clue.
    >
    > However, the page flags you show later on (0x1c) ended up making me take
    > notice of something. That's "dirty", and maybe it's from
    >
    > if (dirtied)
    > SetPageDirty(page);
    >
    > in that same sgl_unmap_user_pages() routine.. And it strikes me that that
    > is bogus.
    >
    > Code like that should use "set_page_dirty()", which does the appropriate
    > callbacks to the filesystem for that page. I wonder if the bug is simply
    > because the ST code just sets the dirty bit without telling anybody else
    > about it...
    >

    It should be using set_page_dirty_lock(). As should st_unmap_user_pages().
    I doubt if this would explain a refcounting problem though.

    Ryan, It might be worth poisoning the thing, see if the completion is being
    called twice:


    diff -puN drivers/scsi/st.c~a drivers/scsi/st.c
    --- devel/drivers/scsi/st.c~a 2006-01-08 21:11:47.000000000 -0800
    +++ devel-akpm/drivers/scsi/st.c 2006-01-08 21:12:13.000000000 -0800
    @@ -4482,11 +4482,12 @@ static int sgl_unmap_user_pages(struct s
    struct page *page = sgl[i].page;

    if (dirtied)
    - SetPageDirty(page);
    + set_page_dirty_lock(page);
    /* FIXME: cache flush missing for rw==READ
    * FIXME: call the correct reference counting function
    */
    page_cache_release(page);
    + sgl[i].page = NULL;
    }

    return 0;
    _
    -
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